Ramires may be out "for at least four weeks at least" due to a medial knee ligament injury suffered during the second half of Chelsea's FA Cup fourth-round victory at Queens Park Rangers.

The injury appeared to happen when the ball hit the Brazilian midfielder's leg. After lengthy treatment by club medical staff he was carried off on a stretcher.

If he is out a month, he could miss at least four Premier League games and the last-16 round of the Champions League when it resumes next month.

André Villas-Boas, the Chelsea manager, said: "It's not so bad in terms of knee injuries. He'll have the MRI on Sunday and we'll know the full extent. Hopefully he is going to avoid an operation and he is going be back soon.

"We have to know the extent of the injury – eventually with treatment we could look at a four-week period, maybe more, hopefully not."

The midfielder is likely to miss the league games with Swansea, Manchester United, Everton and Bolton Wanderers, plus the first leg of the Champions League last-16 encounter with Napoli.

Frank Lampard, who sat out the 1-0 win over QPR with a calf injury, is rated at 50-50 to play against Swansea City on Tuesday.